Buggy code:
public class ProxyControlGui extends LogicControllerGui implements ActionListener , FocusListener , KeyListener , JMeterGUIComponent , UnsharedComponent { private static transient Logger log = LoggingManager . getLoggerForClass ( ) ; private JTextField portField ; private JCheckBox httpHeaders ; private JComboBox groupingMode ; private JCheckBox addAssertions ; private JCheckBox useKeepAlive ; private JComboBox targetNodes ; private DefaultComboBoxModel targetNodesModel ; private ProxyControl model ; private JTable excludeTable ; private PowerTableModel excludeModel ; private JTable includeTable ; private PowerTableModel includeModel ; private static final String CHANGE_TARGET = "change_target" ; private JButton stop ; private JButton start ; private JButton restart ; private static final String STOP = "stop" ; private static final String START = "start" ; private static final String RESTART = "restart" ; private static final String ADD_INCLUDE = "add_include" ; private static final String ADD_EXCLUDE = "add_exclude" ; private static final String DELETE_INCLUDE = "delete_include" ; private static final String DELETE_EXCLUDE = "delete_exclude" ; private static final String INCLUDE_COL = JMeterUtils . getResString ( "patterns_to_include" ) ; private static final String EXCLUDE_COL = JMeterUtils . getResString ( "patterns_to_exclude" ) ; public ProxyControlGui ( ) { } public TestElement createTestElement ( ) { } protected ProxyControl makeProxyControl ( ) { } public void modifyTestElement ( TestElement el ) { } protected void setIncludeListInProxyControl ( ProxyControl element ) { } protected void setExcludeListInProxyControl ( ProxyControl element ) { } private List getDataList ( PowerTableModel model , String colName ) { } public String getStaticLabel ( ) { } public Collection getMenuCategories ( ) { } public void configure ( TestElement element ) { } private void populateTable ( PowerTableModel model , PropertyIterator iter ) { } public void focusLost ( FocusEvent e ) { } public void focusGained ( FocusEvent e ) { } public void actionPerformed ( ActionEvent action ) { } private void startProxy ( ) { } private void enableRestart ( ) { } public void keyPressed ( KeyEvent e ) { } public void keyTyped ( KeyEvent e ) { } public void keyReleased ( KeyEvent e ) { } private void init ( ) { } private JPanel createControls ( ) { } private JPanel createPortPanel ( ) { } private JPanel createTargetPanel ( ) { } private JPanel createGroupingPanel ( ) { } private JPanel createIncludePanel ( ) { } private JPanel createExcludePanel ( ) { } private JPanel createTableButtonPanel ( String addCommand , String deleteCommand ) { } private void reinitializeTargetCombo ( ) { } private void buildNodesModel ( JMeterTreeNode node , String parent_name , int level ) { String seperator = "<seq2seq4repair_space>><seq2seq4repair_space>" ; if ( node != null ) { for ( int i = 0 ; i < ( node . getChildCount ( ) ) ; i ++ ) { StringBuffer name = new StringBuffer ( ) ; JMeterTreeNode cur = ( ( JMeterTreeNode ) ( node . getChildAt ( i ) ) ) ; <START_BUG> TestElement te = cur . createTestElement ( ) ; <END_BUG> if ( te instanceof ThreadGroup ) { name . append ( parent_name ) ; name . append ( cur . getName ( ) ) ; name . append ( seperator ) ; buildNodesModel ( cur , name . toString ( ) , level ) ; } else if ( te instanceof Controller ) { name . append ( spaces ( level ) ) ; name . append ( parent_name ) ; name . append ( cur . getName ( ) ) ; TreeNodeWrapper tnw = new TreeNodeWrapper ( cur , name . toString ( ) ) ; targetNodesModel . addElement ( tnw ) ; name = new StringBuffer ( ) ; name . append ( cur . getName ( ) ) ; name . append ( seperator ) ; buildNodesModel ( cur , name . toString ( ) , ( level + 1 ) ) ; } else if ( ( te instanceof TestPlan ) || ( te instanceof WorkBench ) ) { name . append ( cur . getName ( ) ) ; name . append ( seperator ) ; buildNodesModel ( cur , name . toString ( ) , 0 ) ; } } } } private String spaces ( int level ) { } public void setNode ( JMeterTreeNode node ) { } }

Fix:
TestElement te = cur . getTestElement ( ) ;